This was spurred by https://beta.musicbrainz.org/edit/138962452. The style guidelines are not clear as to how to enter multi-modal mediums such as the DVD side of DualDiscs.
So I might as well ask the community: how many mediums should be used in this situation?
A disk only has two sides. So one medium per side.
Your question is confusing unless one reads the edit notes and sees that you had created a release with three sides on a disk. Splitting the video and audio found on the DVD side into separate mediums. That is confusing.
A normal DVD or Bluray is entered as a single medium. You often find a mixture of audio and video on one DVD disk and it is entered as one medium. (Same with an Enhanced CD now I think about it)
I was wondering what multi-modal mediums meant, and found:
I cannot vote for 1 medium per side, as it would mean to split each cassette and vinyl into 2 mediums. It looks wrong.
I’m pretty sure the intention was always “one medium for the CD side, one for the DVD side”. The description in the formats list (which, still and annoyingly, we don’t seem to really display anywhere yet - I need to get that code merged finally) says: “The CD layer of a DVDplus. The DVD layer should be added as a separate medium.” vs “The DVD (audio) layer of a DVDplus. The CD layer should be added as a separate medium.” / “The DVD (video) layer of a DVDplus. The CD layer should be added as a separate medium.” This strongly suggests having two mediums, but of course it would be a lot clearer if we showed it to users when selecting the format 
DVD Audio and DVD Video are different formats. DVD Audio is distinguished by having content in AUDIO_TS folder. They are not descriptions of the content. The DVD side can only be one or the other, not both.
I have read through the links and other information and I am not sure I can make a proper vote since I am missing information that I need to process this request. I prefer clarity in the database but also want as much of the information to be available (within reason). I have unresolved issues with Hybrid SACD releases which show incomplete in picard due to the second medium. While this is a tagger issue it does open up the question of how others use the release information and possible confusion around it. Also can someone point me to the use of a “pseudo-format”. I have seen this mentioned in the form but do not understand its use.
The vote is confusing out of context as it only really applies to a very specific type of disc.
This is a specific question about these unusual pressed medium that have a different type of disc pressed on each side. CD on one side, DVD on the other.
It is not about two sides of a tape or vinyl as they have the same type of medium on both sides so no problems with entering them as one medium for both sides. The hardware reads both sides of those using the same technology in the reader.
Yes, I did understand this. I was talking about contents of a DVD-Video that can sometimes have audio tracks included but they play with a video that just shows a track name or something. I focus on what is manufactured. 
I can see this is what the confused edit was trying to show as different “medium”. A DVD is a DVD and can only be one type or another.
I see these as having three different mediums manufactured onto one side of the disc and the hardware adjusts as to which layer is being read. This makes sense as why we then have three medium for the three layers. Each layer is encoded with different technology
It is not the case that all DVD’s are alike. You need a DVD Audio capable player to play the DVD Audio content. DVD Audio is a unique format that requires special hardware to read.
We don’t have separate video and audio layers for the same DVD disc, so it seems weird to say a DualDisc could.
Also, Sony/BMG (so Arista, RCA, Epic) specifically didn’t support DVD-A in their DualDiscs because they wanted you to use SACD:
https://www.sony.com/electronics/support/articles/S1Q0059
https://www.sony.com/electronics/support/articles/00006807
https://forums.stevehoffman.tv/threads/dire-straits-brothers-in-arms-sacd-vs-dvd-a.64692/#post-1372606
https://www.reddit.com/r/audiophile/comments/15yj0lv/comment/jxfedz9/
So even if it were possible for a DualDisc’s DVD side to be represented as separate DVD-V and DVD-A mediums, my understanding is this would never be the case for a Sony release. But it seems like the existence of the separate layers are to mirror the existence of DVD-Video and DVD-Audio as mutually exclusive formats, and they aren’t supposed to be used on the same side of a disc.
Sorry for my far too simple reply. Yes I am aware there are many types of DVDs. Same as CDs. And not all players can handle the different types. What I was trying to point out in an over simple way was one side is one side is one medium. And that DVD may be one of many different types of DVD, but only one specific type. They are all DVDs, but not all DVDs are the same.
I was trying, and clearly failing, to stay simple.
No problem. If this stuff was simple we wouldn’t have to discuss it!
Apparently, they can be both at the same time, for convenience:
DVD-Audio - Wikipedia
A common configuration is a single-sided DVD with content in both the DVD-Video (VIDEO_TS) and DVD-Audio (AUDIO_TS) directories.
The point is that the MusicBrainz DVD doesn’t support this in the first place. MusicBrainz DualDisc DVD layer isn’t supposed to do anything that MusicBrainz DVD can’t do.
Yes almost every DVD Audio has DVD Video content. In 99.9% of the cases it mirrors the DVD Audio content but in lossy or non HD form so redundant and confusing to add another medium for it. In that rare case that the content differs I would argue that another medium should be added to represent the difference in content with explanation in the release annotation. I believe there is a Sting DVD Audio where this is the case but I would have to track it down and see how it was handled.